package com.jack.helloworld.util;

class HexUtil {

	private static final char[] DIGITS = {
			'0', '1', '2', '3', '4', '5', '6', '7',
			'8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
	};

	public static String encodeToString(byte[] bytes) {
		char[] encodedChars = encode(bytes);
		return new String(encodedChars);
	}

	public static char[] encode(byte[] data) {
		int l = data.length;
		char[] out = new char[l << 1];
		// two characters form the hex value.
		for (int i = 0, j = 0; i < l; i++) {
			out[j++] = DIGITS[(0xF0 & data[i]) >>> 4];
			out[j++] = DIGITS[0x0F & data[i]];
		}
		return out;
	}

	public static byte[] decode(String hex) {
		return decode(hex.toCharArray());
	}

	public static byte[] decode(char[] data) throws IllegalArgumentException {
		int len = data.length;
		if ((len & 0x01) != 0) {
			throw new IllegalArgumentException("Odd number of characters.");
		}
		byte[] out = new byte[len >> 1];
		// two characters form the hex value.
		for (int i = 0, j = 0; j < len; i++) {
			int f = toDigit(data[j], j) << 4;
			j++;
			f = f | toDigit(data[j], j);
			j++;
			out[i] = (byte) (f & 0xFF);
		}
		return out;
	}

	protected static int toDigit(char ch, int index) throws IllegalArgumentException {
		int digit = Character.digit(ch, 16);
		if (digit == -1) {
			throw new IllegalArgumentException("Illegal hexadecimal charcter " + ch + " at index " + index);
		}
		return digit;
	}
}
